4,223 research outputs found
Graphene under the influence of Aharonov-Bohm flux and constant magnetic field
Investigation of real two-dimensional systems with Dirac-like electronic
behavior under the influence of magnetic field is challenging and leads to many
interesting physical results. In this paper we study 2D graphene model with a
particular form of magnetic field as a superposition of a homogeneous field and
an Aharonov-Bohm vortex. For this configuration, electronic wave functions and
energy spectrum were obtained and it was shown that the magnetic Aharonov-Bohm
vortex plays the role of a charge impurity. As a demonstration of vacuum
properties of the system, vacuum current, as well as an electric current, is
calculated and their representation for particular limiting cases of magnetic
field is obtained
The yoga of commutators
In the present paper we discuss some recent versions of localisation methods
for calculations in the groups of points of algebraic-like and classical-like
groups. Namely, we describe relative localisation, universal localisation, and
enhanced versions of localisation-completion. Apart from the general strategic
description of these methods, we state some typical technical results of the
conjugation calculus and the commutator calculus. Also, we state several recent
results obtained therewith, such as relative standard commutator formulae,
bounded width of commutators, with respect to the elementary generators, and
nilpotent filtrations of congruence subgroups. Overall, this shows that
localisation methods can be much more efficient, than expected
Possible d+id scenario in La_{2-x}Sr_{x}CuO_4 by point-contact measurements
We analyze the results of point-contact measurements in La_{2-x}Sr_{x}CuO_{4}
(LSCO) previously reported as a clear evidence of the separation between gap
and pseudogap in this copper oxide. Here we show that, in addition to this, the
conductance curves of our point-contact junctions -- showing clear Andreev
reflection features -- can be interpreted as supporting a nodeless
d_{x^2-y^2}+id_{xy}-wave symmetry of the gap in LSCO. The results of our
analysis, in particular the doping dependence of the subdominant d_{xy} gap
component, are discussed and compared to the predictions of different
theoretical models.Comment: 6 pages, 4 eps figures, presented at SATT11 Conference (Vietri sul
Mare, March 2002). To appear in Int. J. Mod. Phy
Renormalized theory of the ion cyclotron turbulence in magnetic field--aligned plasma shear flow
The analytical treatment of nonlinear evolution of the shear-flow-modified
current driven ion cyclotron instability and shear-flow-driven ion cyclotron
kinetic instabilities of magnetic field--aligned plasma shear flow is
presented. Analysis is performed on the base of the nonlinear dispersion
equation, which accounts for a new combined effect of plasma turbulence and
shear flow. It consists in turbulent scattering of ions across the shear flow
with their convection by shear flow and results in enhanced nonlinear
broadening of ion cyclotron resonances. This effect is found to lead to the
saturation of ion cyclotron instabilities as well as to the development of
nonlinear shear flow driven ion cyclotron instability. 52.35.RaComment: 21 page
Method of training examples in solving inverse ill-posed problems of spectroscopy
Further development of the method of computational experiments for solving
ill-posed problems is given. The effective (unoverstated) estimate for solution
error of the first-kind equation is obtained using the truncating singular
numbers spectrum of an operator. It is proposed to estimate the magnitude of
the truncation by results of solving model (training, learning) examples close
to the initial example (problem). This method takes into account an additional
information about the solution and gives a new principle for choosing the
regularization parameter and error estimate for equation solution by the
Tikhonov regularization method. The method is illustrated by a numerical
example from the inverse problem of spectroscopy.Comment: 9 pages, 3 figure
- …